Modder ‘y2keeth’ has released Version 2.0 of his Hi Def Mod for Quake 4. According to its description, Quake 4 Hi Def v2.0 updates Quake 4’s graphics by improving the quality of textures and models, as well as shadows.
Going into slightly more details, Quake 4 Hi Def v2.0 adds a bunch of more textures. Moreover, it adds an autoexec.cfg file to crank the detail settings and shader enhancer fast pak file from ng_shaders.
You can download Quake 4 Hi Def v2.0 from here. Below you can also find some screenshots that showcase the improved 3D models and textures.